Add migration startup project note to the tutorial.

docs/en/Tutorials/Part-1.md

@@ -189,6 +189,8 @@ Add-Migration "Created_Book_Entity"
 
 ![bookstore-pmc-add-book-migration](./images/bookstore-pmc-add-book-migration-v2.png)
 
+> If you get an error like "*Your startup project ... doesn't reference Microsoft.EntityFrameworkCore.Design. This package is required for the Entity Framework Core Tools to work*", right click to the `Acme.BookStore.EntityFrameworkCore.DbMigrations` project and **Set as the Startup Project** and try again.
+
 This will create a new migration class inside the `Migrations` folder of the `Acme.BookStore.EntityFrameworkCore.DbMigrations` project.
 
 Before updating the database, read the section below to learn how to seed some initial data to the database.

docs/en/Tutorials/Part-7.md

@@ -70,7 +70,7 @@ This is just like done for the `Book` entity before, so no need to explain again
 
 ## Create a new Database Migration
 
-Open the **Package Manager Console** on Visual Studio and ensure that the **Default project** is `Acme.BookStore.EntityFrameworkCore.DbMigrations` in the Package Manager Console, as shown on the picture below. Also, set the `Acme.BookStore.Web` (or `Acme.BookStore.HttpApi.Host`, depending on your solution) as the **startup project** (right click it on the solution explorer and click to "Set as Startup Project").
+Open the **Package Manager Console** on Visual Studio and ensure that the **Default project** is `Acme.BookStore.EntityFrameworkCore.DbMigrations` in the Package Manager Console, as shown on the picture below. Also, set this project as the **startup project** (right click it on the solution explorer and click to "Set as Startup Project").
 
 Run the following command to create a new database migration: